It is simple enough to apply any type of paint over latex, but to apply latex over an oil-based paint is a little tricky. A wall covered with oil-based paint is usually very smooth. Latex paint will have trouble clinging to-or attaching to-a smooth surface. Even if one succeeds in covering oil paint with latex, the two types of paint expand and contract at different rates, and in a short period of time the paint might chip and peel. The solution is to clean the walls with trisodium phosphate (TSP). TSP is fairly caustic, so remember to wear gloves and goggles. Then apply a super-adherent primer specifically formulated to prime oil paint for latex. There are also super-adherent primers that permit painting over ceramic tiles and plastic laminates. This special primer provides the transition between oil paint and new latex.